Function dwconv 

pub fn dwconv<D: Float>(
    c: usize,
    k: usize,
    s: usize,
) -> impl Fn(SymTensor) -> SymTensor

Depth-wise Conv2d (groups = c) → BatchNorm2d → SiLU.

Matches ultralytics DWConv(c, c, k) with act=True. BN eps=0.001 matching the pretrained YOLO26n weights.